Goudini spa

I am a ATKV member and rarely use my membership. I called for a booking and was told there's no availability, yet when I logged into the website on the same day, there was availability for the dates I requested. I booked immediately and paid as I did not want to lose the booking. I called in immediately to confirm my booking and after a lot of back n forth it was confirmed. At the same time I advised I am a member and have been billed incorrectly as a non-member and it was ignored. I called again and was told that the member rate doesn't apply to my booking as I have already paid. I wrote an email to the Manager and to date haven't received any response from them. Why should I be held liable for an online booking request when the company's website doesn't have the option to add your membership details. I feel very aggrieved and will be canceling my membership as it hasn't given me any benefits. Their terms and conditions do not state if you book on the website you would forfeit your membership discount. How can such a large entity not have an option to correct billing before the person has been on the trip (my booked days are only for next week). This is not ethical and hardly fair business practice.